摘要:

Volume measurement of MgSiO3perovskite was made in the temperature range from 25 to 500°C as a function of pressure up to 20 GPa byin situx‐ray diffraction, using a DIA apparatus combined with synchrotron radiation. The measured thermal expansivity ranges from 1.8 to 2.5*10−5/K and decreases only slightly with pressure. Our present results are in good agreement with the previous lower pressure (up to 11 GPa) data ofWang et al.[1994] and the higher pressure (36 GPa) data ofFunamori and Yagi[1993], but contrast with the results using diamond anvil cell byMao et al.[1991], particularly in a low pressure r

ISSN:0094-8276    

DOI:10.1029/95GL00584

年代:1995

数据来源: WILEY

摘要:

Dehydration reactions can induce excess pore‐fluid pressures that are high enough to affect the mechanical strength and ductility of rocks. Laboratory experiments have been conducted to investigate this phenomenon in dehydrating rocks with porosities that are initially negligible but increase as the reaction progresses. Polycrystalline gypsum samples were first heated under pressure to induce dehydration, then axially loaded after different amounts of reaction. Within the first 1% of reaction, the ultimate strength of the sample decreased and embrittlement was observed. The ultimate strength recovered within 3% of reaction and eventually exceeded that of pure gypsum. Our results indicate that the initial weakening and embrittlement correspond to a pulse of excess pore pressure in the sample interior. Subsequent strengthening is caused by a decrease in pore pressure and the higher strength of the product phas

ISSN:0094-8276    

DOI:10.1029/95GL00886

年代:1995

数据来源: WILEY

摘要:

We demonstrate that the excess dynamic ellipticity of the core‐mantle‐boundary (CMB) inferred from the period of the Earth's retrograde free core nutation (RFCN) may be explained in terms of viscous stresses generated by mantle convective flow. The 3D elastic structure and radial viscosity profile which define the model used in the viscous flow calculations are constrained to simultaneously reconcile a large set of seismic and geodynamic d

ISSN:0094-8276    

DOI:10.1029/95GL01065

年代:1995

数据来源: WILEY

摘要:

The relationship between surface wave magnitude, Ms, and seismic moment, Mo, of earthquakes is essential for the estimation of seismic risk in any region. In the hypothesis of constant stress drop, theoretical models predict that Log Moand Msare related by a linear law. The slope most commonly found in the literature is around 1.5. Here we show that the application to the Msvalues of the necessary correction for the focal depth, gives a general increment of the correlation coefficient, and that a slope around 1.0 is consistent with the global data, while for regionalized data it can vary from about 1.0 to 2.0.

ISSN:0094-8276    

DOI:10.1029/95GL00884

年代:1995

数据来源: WILEY

摘要:

We present a new method for automatic detection and location of seismic events recorded on a network. It is based on a progressive study of the interstation correlation functions, which leads to a consistent set of time‐delays when a seismic phase is present. Three different examples are processed on networks of different size

ISSN:0094-8276    

DOI:10.1029/95GL00468

年代:1995

数据来源: WILEY

摘要:

A largeMw=8.2 earthquake occurred off Shikotan Is., one of the Kurile Is., on October 4, 1994. We inverted 32 body‐wave records to determine the rupture pattern using an iterative deconvolution method. The mechanisms of the subevents were allowed to vary during rupture. The source parameters obtained are: the location of the initial break = (43.48°N, 147.40°E); the centroid depth = 56 km; (strike, dip, rake) = (49°, 75°, 125°) for the total source; the seismic momentMo= 2.6×1021Nm (Mw=8.2); source time durationT= 42 s; the average rupture velocity ν = 2.5 km/s. We also determined the mechanism using long‐period Love and Rayleigh waves from 14 stations. The solution for a finite source distributed over a depth range from 0 to 90 km is (strike, dip, rake) = (54°, 76°, 129°) withMo= 2.3×1021Nm, in good agreement with that from body waves. Referring to the extent of the aftershock area and the subevent distribution, we estimated the fault areaS= 120 × 60 km², the average slipD=5.6m, and the stress drop Δσ=11 MPa. We computed synthetic waveforms as well as static displacements using either the steep or the low‐angle plane as the fault plane, and found that the steep‐dip fault model fits the data better. Our result (the mechanism, large centroid depth, high stress drop) strongly suggests that the 1994 Shikotan earthquake is a lithospheric earthquake: an intra‐plate event that ruptures through a substantial part of the subducting oceanic lithosphere. This type of lithospheric earthqu

ISSN:0094-8276    

DOI:10.1029/95GL00883

年代:1995

数据来源: WILEY

摘要:

New information has been obtained by reanalyzing the rupture process of three large strike‐slip earthquakes that occurred in the Gulf of Alaska on November 17 and 30, 1987 and March 6, 1988. We used spectral analysis of P‐waves complemented with a simple technique for inverting body waves using a fixed source mechanism. Our results show that the Ms=7.0 event of November 17, which can be considered to be a foreshock to the November 30 event, consisted of two pulses of large seismic moment release: the first one with a duration of ∼15 sec coincides with those obtained by other studies; the second, which occurs 20 sec after the first arrival is clearly visible on the records, but was not previously reported. The Ms=7.4 earthquake of November 30 is a complex event that ruptured on a fault plane trending north‐south. The Ms=7.7 shock of March 6, 1988 was a simple event along the same north‐south trend south of the November events. P‐wave far field spectra exhibit an ω−1intermediate trend between the usual ω0and ω−2slopes. This trend is due to rupture along a long, narrow fault, so the corner frequency associated with this intermediate trend is related to the reciprocal of rupture propagation time. We suggest that these events were due to a tear in

ISSN:0094-8276    

DOI:10.1029/95GL00905

年代:1995

数据来源: WILEY

摘要:

Aftershocks of the 1971 San Fernando and 1994 Northridge earthquakes were relocated using a three‐dimensional velocity model that was derived from inverting P‐wave travel time data. The hypocenters show clear orientations of the dipping fault planes. The San Fernando aftershocks form a plane extending from a depth of 15 km to the surface, dipping toward the northeast at about 40°. The Northridge aftershocks delineate a fault extending from a depth of 18 km up to about 5 km, dipping toward the southwest at about 40°. In the region the aftershocks overlap in map view, the San Fernando plane cuts off the Northridge plane at a depth of 5 to 8 km, preventing it from reaching the surface. The similar but oppositely dipping fault planes suggest a pair of conjugate planes reflecting a horizontal northeast‐southwest comp

ISSN:0094-8276    

DOI:10.1029/95GL00712

年代:1995

数据来源: WILEY

摘要:

Using the interferometric fringes generated by the phase difference between a pair of synthetic‐aperture radar (SAR) images acquired by the ERS‐1 satellite, we estimate the focal mechanism of a small, shallow thrust earthquake. The inversion procedure is an iterative, linearized least‐squares algorithm based on a standard elastic dislocation formulation for coseismic displacements. Our preferred estimate is a thrust focal mechanism with its hypocenter at (N34.35° ± 0.4 km, W116.91° ± 0.2 km, 2.6 ± 0.3 km depth) on a plane dipping southward beneath the San Bernardino Mountains, with a moment magnitude (Mw) of 5.4. The strike, dip, and rake are N106°E ± 7°, 28° ± 4°, and 93° ± 4°, respectively on a fault 3.1 ± 0.5 km wide and 2.9 ± 0.4 km long. The precision of these estimates is competitive with seismol

ISSN:0094-8276    

DOI:10.1029/94GL03212

年代:1995

数据来源: WILEY

摘要:

Azimuthal asymmetries in the atmospheric refractive index can lead to errors in estimated vertical and horizontal station coordinates. Generally these gradients are not modeled in standard very long baseline interferometry (VLBI) geodetic analysis. Daily average gradient effects can be as large as 50 mm of delay at a 7° elevation. To model gradients, the constrained estimation of gradient parameters was added to the standard VLBI solution procedure. Here the analysis of two sets of data is summarized: the set of all geodetic VLBI experiments from 1990–1993 and a series of 12 state‐of‐the‐art R&D experiments run on consecutive days in January 1994. In both cases, when the gradient parameters are estimated, the overall fit of the geodetic solution is improved at greater than the 99% confidence level. Repeatabilities of baseline lengths ranging up to 11,000 km are improved by 1 to 8 mm in a root‐sum‐square sense. This varies from about 20% to 40% of the total baseline length scatter without gradient modeling for the 1990–1993 series and 40% to 50% for the January series. Gradients estimated independently for each day as a piecewise linear function are mostly continuous from day to day within their formal

ISSN:0094-8276    

DOI:10.1029/95GL00887

年代:1995

数据来源: WILEY